mc5 - Obscure vault 99 (7)

It's the cryptic crossword discussion game. Tease each other with clues, help each other with the dailies, educate the beginners, whatever.

I was trying to post this last night when MC5 started to go nuts. Seed of the Greenwich time signal (3) In the meantime, Chalky, yes, do letters.

... and again

Slightly pointless expulsion under ruling. [10]
. U . . E . T . . .
Darren - Is it PIP ?

Chalky - yes. Is yours SUBJECTION?

I'll show you mine if you show me yours ....

Darren - absolutely yes. Now, as you seem to know about these things - would my clue have 'held up' even without the letters to guide the way?

Well, "slightly" for SUB took me a while to get. But that's just my failing! "Under" seems a little superfluous to me, though.